The present application is related to applicant""s copending application entitled Glass Ceramic Systems Ser. No.: 10/741,795, filed Dec. 19, 2003, by the same inventors.
The invention relates to the fields of industrial art for making glass and ceramic components, tool and die arts for making molded glass and ceramic components, photostructurable arts for laser milling glass and ceramic components, semiconductor arts for fabricating semiconductors and hybrids, and for depositing conductor traces in an electrical communications grid, microelectromechanical arts for making active and passive MEMS devices, wafer flip and bond art for encapsulating electrical devices, MEMS devices, and optical devices, electrical arts for making batteries, power converters, and RF antennae, electronic arts for making processors, electronic components, optoelectronic interfaces, RF transmitters, RF receivers, and despreading correlators, electromechanical arts for making active gyros, and accelerometers, photonic arts for making optical transceivers, optical detectors, mirrors, splitters, reflectors, polarizers, lenses, and optical fibers for communicating and processing optical signals for use in an optical communications grid, all for use and incorporation into a new field of integrated glass ceramic systems having structural elements formed from molded and patterned glass ceramic materials with internally communicated optical and electrical signals while also having encapsulated electronic, photonic, electrical and microelectromechanical system devices intercommunicating through an internal electrooptical communications grid.
There are a vast variety of conventional fabrication methods and devices used from a variety of operational systems. As examples, industrial arts have been used for making glass and ceramic components. The tool and die arts have been used for making molded glass and ceramic components. Molded components include poured, injected and stamped glass ceramic components. The semiconductor arts have been used for fabricating semiconductors, chips, and hybrids. During fabrication, depositing conductor traces and with feedthroughs are used to form an electrical communications grid about the semiconductor components. The microelectromechanical systems (MEMS) arts have been used for making active and passive MEMS sensors and actuators, among others devices. The wafer flip and bond arts have been used for electrically connecting and encapsulating electrical devices, MEMS devices, and optical devices within flip-bonded semiconductor and ceramic substrates. The electrical arts have been used for making batteries, power converters, communications processors, and RF antennae, among others. The electronic arts have been used for making power supplies, electronic devices, optoelectronic devices, RF transmitters, RF receivers, and despreading correlators, among others. The electromechanical arts have been used for making active gyros, and accelerometers, among others. The photonic arts for have been used for making optical transceivers, optical detectors, mirrors, splitters, reflectors, polarizers, lens, and optical fibers, among others, for communicating and processing optical signals for use in an optical communications grid. While there is a vast array of technologies available, system integration of various technology is limited due to operational compatibility and fabrication feasibility.
One example of an intertechnology integrated system is a conventional satellite. A satellite can be made of silicon for exploiting strength, high thermal conductivity, infrared transparency, and radiation-shielding properties of silicon along with established silicon microelectronics and microelectromechanical systems fabrication techniques to create satellites composed of silicon components. Silicon is an excellent choice as the main material for a spacecraft, but bulk mechanical, thermal, and optical properties cannot be significantly modified.
Glass materials have an amorphous state that is a noncrystalline state. Ceramic materials have a crystalline state. Ceramic materials are tougher than glass but also tend to be more brittle than the glass, and hence not generally suitable as a support structure in high tensile stress application. Glass is weaker than ceramic, and susceptible to breakage during wide temperature operating range variations, but glass has superior optical transmission characteristics and can be brittle. Ceramics can withstand higher temperatures than the glass, but have poor optical transmission characteristics. Glass and ceramic materials differ in material properties, such optical transmission, electrical conductivity, thermal conductivity, and chemical resistance, offering operational incompatibility, and unsuitability for common use in a given application. Glass materials have been annealed to reduce internal stresses and prevent cracking and breakage during cooling, especially for thick components. This is typically accomplished by heating glass to its softening temperature, followed by a slow cool-down process. Annealing decreases the overall strength of glass, but also makes the glass less brittle. Ceramic materials can also be annealed, but it is usually used to improve strength. Ceramic annealing changes crystal grain size. Glass materials have been tempered to increase internal compressive stresses for increasing the strength of the glass to external tensile loads. This is typically accomplished by heating glass to its softening temperature, followed by a rapid cool-down process. Ceramic materials are not tempered.
Glass ceramic materials have portions in the amorphous state and portions in the crystalline state. Glass ceramic materials incorporate an in-situ nucleation process that results in the crystallization of the amorphous glass phase. This conversion process is nominally called devitrification. Typically, glass stock is produced with additional ingredients that upon heating above a specified temperature, induces ceramization of the material. The bake method provides a material that is controllably devitrified, that is, a controlled in situ precipitation of crystalline material within an amorphous glass body. Beyond the known advantages of glass and ceramics, glass ceramic materials offer cost-effective manufacturing of shaped ceramic parts. The initial material in the glass phase is melted and molded into the desired shape and then converted to the crystalline ceramic state. Because the resulting material is not 100% crystalline, but a composite of amorphous and crystalline phases, it is less brittle than true crystalline ceramics. Glass ceramic materials are used in a wide range of applications from specialized optics to consumer cookware. Some well-known trade names are Macor which is machinable ceramic Corning Corporation, Dicor which is a biomaterial from Corning Corporation, Zerodur which is an expansion material from Schott Corporation, ML-05 which is a magnetic material from Nippon Electric Glass Company, and Pyroceram which is a cookware material from Corning Ware.
A special category of sensitized glass ceramic material is the photostructruable glass ceramic materials, also called photositalls and photocerams. Photostructruable glass ceramic materials differ from most glass ceramic materials in that photosensitive agents are incorporated into the raw material. Upon photo excitation, these agents initiate a reaction that can lead to nucleation and crystallization, that is, ceramization, of the glass during a controlled bake process. One set of bake cycles leads to the formation of a metastable crystalline state which is soluble in hydrofluoric acid (HF). Another set of bake cycles leads to the formation of a stable crystalline state that is resistant to etching by both acids and bases. Photostructurable glass ceramic materials can be photolithographically patterned, and upon baking, only those patterned areas would be converted to one of the ceramic states. The exposure process is typically done using a flood-fill light source through an opaque mask resting directly on top of the photostructurable glass ceramic material. Patterning of the photostructurable glass ceramic material can be done by creating the metastable state and etching away this state in HF. An additional flood exposure and bake to the stable crystalline state will result in a patterned ceramic component. One example of a photostructurable glass ceramic material is Foturan of Schott Glass Works, Mainz, Germany that requires ultraviolet light for photoexposure and baking to temperatures above 500C.
Photostructurable glass ceramic materials can also be patterned using lasers that selectively expose parts of the material. Photostructurable glass ceramic materials can be micromachined with three-dimensional precision as an optically patterned component by direct-write laser milling, direct-write laser exposure followed by a chemical etching step to remove exposed volumes, or by photolithographic patterning followed by a chemical etching step to remove patterned areas.
The photostructurable glass ceramic material can be used to make components for various applications. For example, photostructurable glass ceramic materials have been used as a substrate and structure component in a multi-thruster propulsion system for a spacecraft also having metallic structural components with coupled semiconductor electronics on printed circuit boards. The propellant tank, propellant feed lines, and thrusters are all composed of micromachined photostructurable glass ceramic material, while the remaining components include batteries, electromagnetic solenoid valves, the pressure and temperature sensors, the fill and drain valves, and the electronics. The glass ceramic thruster substrate is supported in a metallic support structure providing structural support for the spacecraft. One problem associated with conventional metallic support structure is the mix of various supporting components and their various differences in thermal expansion coefficients, thermal conductivity, and optical properties that need to considered over the operational temperature ranges. In addition, silicon and metallic support structures require the use of harnesses and cables to route electrical lines about the spacecraft. In addition, silicon and metallic support structures block visible optical transmission, limiting optical communications paths about the silicon or metallic support structures. Further, silicon and metallic support structures have different material strengths rendering portions providing uneven structural strength about the support structure. Further still, silicon and metallic support structures have limited molding and precise patterning manufacturing methods. These and other disadvantages are solved or reduced using the invention.
An object of the invention is to provide an integrated glass ceramic system having mixed glass ceramic components being molded and patterned glass and ceramic components for providing a variety of structural shapes.
Another object of the invention is to provide an integrated ceramic system having a support structure consisting of glass and ceramic components.
Yet another object of the invention is to provide an integrated glass ceramic system having glass ceramic composite components with tempered and untempered glass portions for providing enhanced structural strength.
Still another object of the invention is to provide an integrated glass ceramic system having a plurality of glass ceramic support structures integrated together for supporting an electrical and electronic communications grid.
A further object of the invention is to provide an integrated glass ceramic system having a plurality of glass ceramic support structures that are transmissive to various optical wavelengths for providing an optical communications grid.
Yet A further object of the invention is to provide an integrated glass ceramic system having a plurality of glass ceramic support structures that are transmissive to various wavelengths for providing an internal optical communications grid and for supporting an internal electrical and electronic communications grid combined as an electrooptical communications grid that includes structured glass sensors and actuators.
The invention is directed to integrated glass ceramic systems, in the general form, having patterned glass ceramic components having tempered and untempered portions within composite components, which when integrated together, form a glass ceramic support structure supporting an electrooptical communications grid while encapsulating and supporting operational components, such as photonic, electronic, electrical, and microelectromechanical (MEMS) devices. The direct-write glass ceramics components can be laser-milled, laser exposed and etched, or photolithographicly illuminated and etched glass ceramic components. In a preferred form, an integrated glass ceramic system is a glass ceramic spacecraft having a plurality of molded and patterned components integrated together for forming a support structure through and on which is supported the electrooptical communications grid.
The unique attributes of photostructurable glass ceramic materials include adapting the material for high transparency in the visible through the near IR wavelengths, designing the material for multifunctionality by locally altering a physical property, and by processing the material for patterned metallization. These attributes permit a wide range of functions that can serve the structural, thermal, electrical, and optical requirements of an integrated glass ceramic system. By selectively controlling the material processing, the photostructurable glass ceramic materials can simultaneously function as support structures, thermal control systems, radiation shields, optical conduits, multichip substrates, photonic supports, electronics supports, antenna supports, sensor structure, sensor support, actuator structure, actuator support, and microelectromechanical systems supports. This multifunctionality allows an entire integrated glass ceramic system to be substantially fabricated from a single material while supporting a plurality of integrated photonic, electronic, electrical, and MEMS devices. These capabilities offer predetermined consistent material strength, optical properties, electrical properties, thermal properties, and chemical properties. Composite ceramic structures can be fabricated through localized ceramization down to the micron scale. The photostructurable glass ceramic materials can have a glass phase that can be used for visible through near infrared optics passing wavelengths typically between 0.35 xcexcm to 2.8 xcexcm. Photostructurable glass formulations can be designed to enhance or extend these wavelength ranges. The photostructurable glass ceramic materials can be manufactured using molding and patterning methods to any dimension and to any shape.
The glass state in photostructurable glass ceramic materials can be tempered for improved strength by using a rapid cool-down process after baking. Another way to increase tensile strength is by selective exposure to light with subsequent baking to create crystalline domains in the glass. The crystalline domains in this composite material are stronger than the glass and their decreased density, compared to the glass state, generates a local compressive stress.
Glass ceramic materials include sensitized glass, thermally-tempered glass having increased internal stress for increased strength, crystal-tempered glass ceramic composites for increased strength, annealed glass having decreased internal stresses and smooth surface for enabling system integration, and ceramics having crystalline states made from sensitized amorphous glass. Glass and ceramics can have increased tempering in areas where high mechanical strength is desired, and can have reduced tempering in areas where mechanical or vibration compliance is desired or where a clearer optical path is desired or properties are desired that are more commensurate of the glass state of the original glass formulation. Ceramics can withstand higher temperatures and stresses than glass. A composite glass ceramic material can also be thermally-tempered to provide a more uniform stress response to a given load for improved mechanical toughness.
Photostructurable glass ceramic materials can be used to make spacecraft support structure, insulated circuit substrates, multichip module supports, actuators, sensors, and thermal control systems providing simultaneous multifunctionality. Almost all of the dry mass of a spacecraft, except for batteries and propellant, for example, can be composed of photostructurable glass and ceramic materials supporting operational photonic, electronic, electrical and MEMS devices. In the glass state, photostructurable glass and ceramic materials can be molded into any shape using low cost forming techniques, micromachined or macromachined to micron tolerances, metalized for forming an electronics communications grid, and then assembled into an integrated glass ceramic system through fusion bonding. The multifunctional properties of the photostructurable glass and ceramic materials and available low cost fabrication techniques enable photostructurable glass and ceramic materials to be used as a support structure in low-cost reproducible satellites. When tempered, the photostructurable glass and ceramic materials have substantially increased reliability against tension-induced fracture. Localized tempering can provide additional strength in a support structure where additional support strength is desirable. Tempered photostructurable glass and ceramic materials are electrical insulators, thermal insulators, and are transparent to visible through near IR light in the glass and glass ceramic composite phases.
That is, the photostructurable glass ceramic materials can be molded and patterned into any shape and composition, resulting in a wide range of structural, thermal, electrical, and optical properties. This multifunctionality allows almost an entire integrated spacecraft to be fabricated from photostructurable glass ceramic material. The photostructurable glass ceramic materials are amenable to material handling requirements found during conventional manufacturing. The photostructurable glass ceramic materials do not outgas chemicals, have zero porosity, and can be handled using clean-room protocols, and are therefore amenable to system integration using standard microelectronics fabrication processes. Valves, sensors, and actuators could also be fabricated using photostructurable glass ceramic materials with applied metal or polysilicon layers to provide electrodes or resistive structures for sensing and actuation.
A satellite can be made primarily of photostructurable glass ceramic materials with supported electronic, electrical, photonic, and MEMS devices. Spacecraft photonics and electronics are preferably integrated onto and encapsulated by glass ceramic substrates that multifunction as circuit boards. The encapsulation provides limited prevention of contamination. For example, a stack of integrated glass ceramic substrates can multifunction as a support structure while providing interface layers on which and through which are deposited conducting interconnects for forming an electrical communications grid about the support structure, and while providing internal optical paths for optical communication between optical transceivers for forming an optical communications grid about the support structure. Optical communications between and through the glass ceramic substrates of the support structure is enabled due to the wide transparency range of the glass phase of the photostructurable glass ceramic materials. Specific regions and volumes of the support structure are converted into the ceramic phase to provide enhanced dielectric properties for microwave circuits or to provide additional strength, while other regions and volumes are converted into the glass phase to provide enhanced internal optical communications.
The spacecraft thermal control for a glass ceramic satellite is very different from a silicon or metallic satellite. Photostructurable glass ceramic materials can have a low thermal conductivity of 1.35 W/m-K for the glass phase which is less than stainless steel or aluminum used in conventional spacecraft. Due to the optical and near infrared transparency of the photostructurable glass ceramic materials, less than ten percent of received solar energy will be absorbed in the material while almost all of the infrared energy from the earth will be absorbed. This thermal absorption smoothes the temperature ranges for a satellite in Earth orbit where a significant fraction of the orbit is in eclipse. The high thermal insulating aspects of photostructurable glass ceramic materials can be thermally limiting for high power components, such as microprocessors and communication circuits. Fabrication of three-dimensional micro heat pipes, which are metalized and help to direct the heat away from these sources, can mitigate this thermal limitation of the photostructurable glass ceramic materials. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.